The invention relates to carbon-containing plate-like pigments and to processes for their preparation and to their use.
Plate-like substrates, such as, for example, metals, metal oxides or plate-like materials coated with metal oxides are used in many technical fields. The incorporation of carbon in pigments produces particular coloring effects. These carbon-containing pigments are used not only for pigmenting paints, powder coatings, varnishes, printing inks, plastics and the like but also in cosmetic preparations.
The only prior method for preparing combinations of carbon/metal oxide mica pigments consists in applying carbon from an aqueous suspension using suitable surface-active auxiliaries or by pyrolysis of organic compounds. DE-AS 11 65 182 describes a complicated pyrolysis process, in which the carbon black is naturally only deposited on the pigment surface. In the process described in German Patent 25 57 796, a substrate is first mixed with a carbon black dispersion. The addition of a metal salt solution under hydrolysis conditions precipitates a carbon black-containing metal hydroxide layer on the substrate.
However, it has been found that the dried pigments are unsuitable for various applications, since they are not sufficiently wear-resistant. This property is extremely desirable especially for incorporation in cosmetics.
A further disadvantage is the frequently observable bleeding of the carbon black when the pigments are suspended in organic solvents for preparing coating systems.
Furthermore, these pigments are distinguished by a large decrease in luster, caused by adsorption and scattering phenomena of the coarsely divided, precipitated carbon black agglomerates.
Accordingly, there was a need for preparing carbon-containing pigments of high wear resistance, which have special coloring effects due to their carbon content and whose preparation does not require large technical expenditure. This object could be achieved by means of the present invention.